Synthetic loss measurements using session numbers

ABSTRACT

A method and system for performing synthetic loss measurements (SLM) includes methods for single-ended and dual-ended synthetic loss measurements. The methods include maintaining a session number indicative of a physical network component at each maintenance point used to perform synthetic loss measurements. The session numbers are maintained according to a novel protocol and are used to detect a change in the network component, such as resulting from a protection switch event. The session numbers enable the synthetic loss measurements to continue irrespective of changes in the values for the session numbers and to remove errors when computing frame loss that may arise when physical network components change. The disclosed methods and systems may be used when a link aggregation group exists between a local maintenance point and a remote maintenance point.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/860,365 filed Apr. 10, 2013, the contents of which is herebyincorporated in its entirety by reference.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to communications systems and morespecifically to synthetic loss measurements using session numbers.

2. Description of the Related Art

A communication network may include network elements that route packetsthrough the network. Some network elements may include a distributedarchitecture, wherein packet processing may be distributed among severalsubsystems of the network element (e.g., line cards).

Service Operation, Administration, and Management (“Service OAM” or“SOAM”), is defined by ITU-T Y.1731/IEEE 802.1ag and defines MaintenanceEntity Group End Points (MEPs) and Maintenance Entity Group IntermediatePoints (MIPs) that may be provisioned on a network element. Throughoutthis disclosure, MEPs and MIPs may generally be referred to as“maintenance points.” A maintenance point may be associated with aparticular maintenance level (e.g., 0 to 7) and may be configured tocommunicate traffic to a peer maintenance point at the same maintenancelevel that resides in the communication network. The maintenanceentities of a maintenance entity group are maintenance points comprisingend points (e.g., MEPs) and intermediate points (e.g., MIPs). Themaintenance points may represent entities that are provisioned within anetwork element. An end point is a maintenance functional entityimplemented at the ends of a maintenance entity group. An end point maygenerate and receive packets such as OAM frames. An intermediate pointrepresents a maintenance functional entity between end points. Anintermediate point responds to packets received from end points and mayforward these packets to downstream intermediate points and end points.

From time to time, maintenance points may perform data loss measurementsto characterize network performance between two or more MEPs. The dataloss measurements may be employed using payload data or using syntheticdata, the latter of which is also referred to as synthetic lossmeasurement (SLM) as specified by ITU Y.1731. During synthetic lossmeasurement, synthetic data frames are transmitted between at least twoMEPs and are counted by at least one receiving MEP. By counting theactual number of transmitted and received synthetic data frames during ameasurement period, a frame loss ratio and/or other frame loss parametermay be determined and may be used to characterize performance of themeasured network segment.

In various embodiments, network elements may also employ linkaggregation. Link aggregation (e.g., as specified by IEEE 802.1AX-2008)may generally describe the practice of using multiple network cables orports in parallel to increase the link speed beyond the limits of anyone single cable or port, and to increase redundancy for higheravailability. In link aggregation, a group or set of ports may becombined and represented as a single logical port to other components ofthe network system. Various switching elements of the network system may“see” the aggregated ports (known as a “link aggregation group” or“LAG”) as a single logical communication port in the routing tables ordatabases of network elements external to the LAG.

In equipment that is undergoing a conventional synthetic lossmeasurement, a lack of statefulness among MEPs may result in measurementerrors. This kind of measurement error may occur in various kinds ofnetwork equipment and particularly when the transmitting and receivingMEPs do not otherwise share state information with each other.

SUMMARY

In one aspect, a disclosed method for performing dual-ended syntheticloss measurements includes maintaining, at a local maintenance point, atransmitting session number for a first interface component associatedwith the local maintenance point and a receiving session number for asecond interface component associated with a remote maintenance point,and receiving, at the first interface component, a first one-waysynthetic loss (1SL) frame from the second interface component. Thefirst 1SL frame may include a first session number indicative of thesecond interface component. When the first session number does not equalthe receiving session number, the method may include copying the firstsession number to the receiving session number, and resetting anincoming frame count at the local maintenance point. The incoming framecount may be indicative of a number of 1SL frames received from thesecond interface component.

In some embodiments, the method includes detecting deactivation of thefirst interface component and activation of a third interface componentassociated with the local maintenance point. The operation of detectingmay include assigning a second session number to the third interfacecomponent, and assigning a third session number to the first interfacecomponent. The second session number and the third session number may bedifferent from the transmitting session number. Responsive to receiving,from the second interface component, a second 1SL frame including thefirst session number, at the third interface component, the method mayinclude determining when at least one session condition is true. Thesession conditions may be selected from the following sessionconditions: the second session number does not equal the transmittingsession number, and the first session number does not equal thereceiving session number. When at least one of the session conditions istrue, the method may include copying the second session number to thetransmitting session number, and copying the first session number to thereceiving session number.

In particular embodiments, the method may include detecting reactivationof the first interface component and deactivation of the third interfacecomponent, while the first interface component replaces the thirdinterface component. The method may include copying the third sessionnumber to the transmitting session number. The method may also includesending, from the first interface component, a third 1SL frame to thesecond interface component, while the third synthetic frame may includethe transmitting session number. The receiving the first synthetic frameand the sending the third synthetic frame may be performed irrespectiveof changes to the transmitting session number and the receiving sessionnumber. The method may still further include calculating a frame lossparameter based on frame count values, including the incoming framecount, for a measurement period, while the frame count values used tocalculate the frame loss parameter may be associated with identicalvalues for the transmitting session number and with identical values forthe receiving session number. The frame count values used to calculatethe frame loss parameter may be associated with identical values for atest identification parameter. The first interface component and thethird interface component may be network interface cards comprising aplurality of network ports. The first interface component and the thirdinterface component may be network ports. The first 1SL frame may be a1SL message that includes the first session number in anorganization-specific type, length, and value (TLV) field in accordancewith the International Telecommunication Union (ITU) Y.1731 standard. Anetwork segment transmitting the first 1SL frame between the firstnetwork element and the second network element may include at least onelink aggregation group (LAG).

Additional disclosed aspects for performing dual-ended synthetic lossmeasurements include a system and an article of manufacture comprisingnon-transitory computer readable memory media storingprocessor-executable instructions.

In another aspect, a disclosed method for performing single-endedsynthetic loss measurements includes maintaining, at a local maintenancepoint, a transmitting session number for a first interface componentassociated with the local maintenance point and a receiving sessionnumber for a second interface component associated with a remotemaintenance point, and sending, from the first interface component, afirst synthetic loss message to the second interface component. Thefirst synthetic loss message may include a first session numberindicative of the first interface component. The method may includereceiving, at the first interface component, a first synthetic lossresponse from the second interface component. The first synthetic lossresponse may include a second session number and a third session numberindicative of the second interface component. When the third sessionnumber does not equal the receiving session number, the method mayinclude copying the third session number to the receiving sessionnumber.

In some embodiments, the method may include detecting deactivation ofthe first interface component and activation of a third interfacecomponent associated with the local maintenance point, while the thirdinterface component replaces the first interface component. The methodoperations of detecting replacement may include assigning a fourthsession number to the third interface component, and assigning a fifthsession number to the first interface component. The fourth sessionnumber and the fifth session number may be different from thetransmitting session number. The method may include sending, from thethird interface component, a second synthetic loss message to the secondinterface component. The second synthetic loss message may include thefourth session number indicative of the third interface component.Responsive to receiving, from the second interface component, a secondsynthetic loss response at the third interface component, while thesecond synthetic loss response may include a sixth session number and aseventh session number indicative of the second interface component, andwhen the sixth session number does not equal the transmitting sessionnumber, the method may further include copying the sixth session numberto the transmitting session number.

In particular embodiments, the method may include calculating a frameloss parameter based on frame count values for a measurement period,while the frame count values used to calculate the frame loss parameterare associated with identical values for the transmitting session numberand with identical values for the receiving session number. The framecount values used to calculate the frame loss parameter may beassociated with identical values for a test identification parameter.The method operations of sending the first synthetic loss message andthe receiving the first synthetic loss response may be performedirrespective of changes to the transmitting session number and thereceiving session number. The first interface component and the thirdinterface component may be network interface cards comprising aplurality of network ports. The first interface component and the thirdinterface component may be network ports. The first synthetic lossmessage may include the first session number in an organization-specifictype, length, and value (TLV) field in accordance with the InternationalTelecommunication Union (ITU) Y.1731 standard. The first synthetic lossresponse may respectively include each of the second session number andthe third session number in an organization-specific type, length, andvalue (TLV) field in accordance with the International TelecommunicationUnion (ITU) Y.1731 standard.

In different embodiments, the method operation of sending, from thefirst interface component, the first synthetic loss message may includesending the first synthetic loss message to a plurality of interfacecomponents associated with a respective plurality of remote maintenancepoints, the plurality of interface components including the secondinterface component. A network segment transmitting the first syntheticloss message between the first interface component and the secondinterface component may include at least one link aggregation group(LAG).

Additional disclosed aspects for performing single-ended synthetic lossmeasurements include a system and an article of manufacture comprisingnon-transitory computer readable memory media storingprocessor-executable instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of selected elements of an embodiment of anetwork;

FIG. 2 is a block diagram of selected elements of a network segmentincluding a link aggregation group;

FIG. 3 is a transaction diagram of selected elements of an embodiment ofa method for dual-ended synthetic loss measurements;

FIG. 4 is a transaction diagram of selected elements of an embodiment ofa method for single-ended synthetic loss measurements;

FIGS. 5A-5C are flowcharts depicting selected elements of an embodimentof a method for dual-ended synthetic loss measurement; and

FIGS. 6A-6C are flowcharts depicting selected elements of an embodimentof a method for single-ended synthetic loss measurement.

DESCRIPTION OF PARTICULAR EMBODIMENT(S)

In the following description, details are set forth by way of example tofacilitate discussion of the disclosed subject matter. It should beapparent to a person of ordinary skill in the field, however, that thedisclosed embodiments are exemplary and not exhaustive of all possibleembodiments.

As used herein, a hyphenated form of a reference numeral refers to aspecific instance of an element and the un-hyphenated form of thereference numeral refers to the collective or generic element. Thus, forexample, widget 12-1 refers to an instance of a widget class, which maybe referred to collectively as widgets 12 and any one of which may bereferred to generically as a widget 12.

Turning now to the drawings, FIG. 1 is a block diagram showing selectedelements of an embodiment of network 100. In certain embodiments,network 100 may be an Ethernet network. Network 100 may include one ormore transmission media 12 operable to transport one or more signalscommunicated by components of network 100. The components of network100, coupled together by transmission media 12, may include a pluralityof network elements 102. In the illustrated network 100, each networkelement 102 is coupled to four other nodes. However, any suitableconfiguration of any suitable number of network elements 102 may createnetwork 10. Although network 100 is shown as a mesh network, network 100may also be configured as a ring network, a point-to-point network, orany other suitable network or combination of networks. Network 10 may beused in a short-haul metropolitan network, a long-haul inter-citynetwork, or any other suitable network or combination of networks.

Each transmission medium 12 may include any system, device, or apparatusconfigured to communicatively couple network devices 102 to each otherand communicate information between corresponding network devices 102.For example, a transmission medium 12 may include an optical fiber, anEthernet cable, a T1 cable, a WiFi signal, a Bluetooth signal, or othersuitable medium.

Network 100 may communicate information or “traffic” over transmissionmedia 12. As used herein, “traffic” means information transmitted,stored, or sorted in network 100. Such traffic may comprise optical orelectrical signals configured to encode audio, video, textual, and/orany other suitable data. The data may also be transmitted in asynchronous or asynchronous manner, and may be transmitteddeterministically (also referred to as ‘real-time’) and/orstochastically. Traffic may be communicated via any suitablecommunications protocol, including, without limitation, the Open SystemsInterconnection (OSI) standard and Internet Protocol (IP). Additionally,the traffic communicated via network 100 may be structured in anyappropriate manner including, but not limited to, being structured inframes, packets, or an unstructured bit stream.

Each network element 102 in network 100 may comprise any suitable systemoperable to transmit and receive traffic. In the illustrated embodiment,each network element 102 may be operable to transmit traffic directly toone or more other network elements 102 and receive traffic directly fromthe one or more other network elements 102. Network elements 102 will bediscussed in more detail below with respect to FIG. 2.

Modifications, additions, or omissions may be made to network 100without departing from the scope of the disclosure. The components andelements of network 100 described may be integrated or separatedaccording to particular needs. Moreover, the operations of network 100may be performed by more, fewer, or other components.

For purposes of SOAM, a service provider operating network 100 maydesire to characterize performance of network 100. For example, aservice agreement with an end user (not shown) may specify a certainlevel of performance, such as in terms of data throughput, latency, anddata errors. The actual network performance provided by network 100 maybe associated with financial considerations for the service provider.For at least such purposes, the service provider may seek to measure, atleast from time to time, a number of data frames that are lost whentransmitted across network 100.

For the purposes of characterizing frame (or packet) loss withinnetworks, such as network 100, the International Telecommunication Union(ITU) has published standards (Y.1731) for performing frame lossmeasurements. One type of frame loss measurement described by Y.1731 isa synthetic loss measurement (SLM) where synthetic (i.e., artificial)frames are inserted between at least two MEPs and are counted by areceiving MEP, as will be described in further detail herein.

Referring now to FIG. 2, a block diagram of selected elements of anembodiment of network segment 200 is illustrated. Network segment 200may represent a portion of network 100 (see FIG. 1). Although networksegment 200 is depicted with three network elements 102 for descriptiveclarity in FIG. 2, it is understood that network segment 200 may includeany number of network elements 102. As shown, network segment 200 mayrepresent a network segment formed between network element 102-1 andnetwork element 102-2, as well as a network segment formed betweennetwork element 102-2 and network element 102-3. Network element 102-1includes processor 208-1 and memory media 210-1, along with networkinterface 204-1 having ports 206-1 and network interface 204-2 havingports 206-2. Network interface 204-1 may be provisioned with maintenancepoint 212-1, while network interface 204-2 may be provisioned withmaintenance point 212-2. When network element 102-1 (or a componentthereof) is configured as an end point in a maintenance entity group,maintenance points 212-1 and 212-2, either individually or incombination, may instantiate a MEP. Network element 102-2, which is anintermediate network element in network segment 200, includes processor208-2 and memory media 210-2, along with network interface 204-3 havingports 206-3, network interface 204-4 having ports 206-4, and networkinterface 204-5 having ports 206-5. Network interface 204-3 may beprovisioned with maintenance point 212-3, network interface 204-4 may beprovisioned with maintenance point 212-4, and network interface 204-5may be provisioned with maintenance point 212-5. As shown, networkelement 102-2 may be an intermediate point in a maintenance entity groupsuch that maintenance points 212-3, 212-4, and 212-5 may instantiateMIPs. Network element 102-3 includes processor 208-3 and memory media210-3, along with network interface 204-6 having ports 206-6. Networkinterface 204-6 may be provisioned with maintenance point 212-6. Whennetwork interface 204-6 (or a component thereof) is configured as anendpoint in a maintenance entity group, maintenance point 212-6 mayinstantiate a MEP.

As depicted in FIG. 2, each network element 102 may include processor208 and memory media 210 that may store instructions executable byprocessor 208. As shown, memory media 210 may represent volatile,non-volatile, fixed, and/or removable media, and may be implementedusing magnetic and/or semiconductor memory. Memory media 210 is capableof storing instructions (i.e., code executable by processor 208) and/ordata. Memory media 210 and/or at least a portion of contents of memorymedia 210 may be implemented as an article of manufacture comprisingnon-transitory computer readable memory media storingprocessor-executable instructions. Memory media 210 may storeinstructions including an operating system (OS), which may be any of avariety of operating systems, such as a UNIX variant, LINUX, a MicrosoftWindows® operating system, or a different operating system. It is notedthat network interface 204 may also include a processor and memory media(not shown) in certain embodiments. A processor and memory included withnetwork element 102, such as processor 208 and memory media 210 oranother processor and memory media, may implement novel methods forsynthetic loss measurements as described herein (see also FIGS. 3A-3C,4A-4C, 5, and 6).

In FIG. 2, network elements 102 are shown including at least one networkinterface 204, which provides a plurality of ports 206 that receive acorresponding transmission media 12 (see also FIG. 1). Ports 206 andtransmission media 12 may represent galvanic and/or optical networkconnections. Each network interface 204 may include any suitable system,apparatus, or device configured to serve as an interface between anetwork element 102 and transmission medium 12. Each network interface204 may enable its associated network element 102 to communicate withother network elements 102 using any of a variety of transmissionprotocols and/or standards. Network interface 204 and its variouscomponents may be implemented using hardware, software, or anycombination thereof. In certain embodiments, network interfaces 204 mayinclude a network interface card. In various embodiments, networkinterfaces 204 may include a line card. Each port 206 may include asystem, device or apparatus configured to serve as a physical interfacebetween corresponding transmission medium 12 and network interface 204.In some embodiments, port 206 may comprise an Ethernet port. Although inFIG. 2 network interfaces 204 are shown with 2 instances of ports 206for descriptive clarity, in different embodiments, network interfaces204 may be equipped with different numbers of ports 206 (e.g., 4, 6, 8,16 ports, etc.). In various embodiments, network element 102 may beconfigured to receive data and route such data to a particular networkinterface 204 and/or port 206 based on analyzing the contents of thedata and/or based on a characteristic of a signal carrying the data(e.g., a wavelength and/or modulation of the signal). In certainembodiments, network element 102 may include a switching element (notshown) that may include a switch fabric (SWF).

As shown in FIG. 2, network segment 200 may represent at least a portionof a network channel in network 100 (see FIG. 1) that includes linkaggregation group (LAG) 220, formed between network element 102-1 andnetwork element 102-2. Although network segment 200 is shown with asingle intermediate network element (network element 102-2), in practicea number of intermediate network elements and corresponding channelsegments may be implemented in various embodiments. As shown in FIG. 2,one of port 206-1 of network element 102-1 and one of port 206-2 ofnetwork interface 204-2 and the corresponding transmission media 12 aregrouped into LAG 220. While LAG 220 is depicted in FIG. 2 as includingtwo of member ports 206 for descriptive purposes, it is noted that invarious embodiments, LAG 220 may include any suitable number of memberports 206. LAG 220 may combine its member ports or member LAGs usinglink aggregation such that the member ports are represented as a singlelogical port of network segment 200. Also, while LAG 220 is shown in aparticular network arrangement in FIG. 2, in different embodiments, LAG220 may be implemented using different network arrangements and/ortopologies. In the embodiment shown in FIG. 2, LAG 220 may appear as asingle logical port to processor 208-1 of network element 102-1 and/orto processor 208-2 of network element 102-2. As noted, variousimplementations and/or configurations of LAG 220 using at least oneintermediate network element may be used in particular embodiments.

In operation of network segment 200 to perform conventional syntheticloss measurements, for example, between maintenance points 212-1, 212-2(referred to collectively as MEP1) and maintenance point 212-6 (referredto as MEP2), a lack of statefulness between MEP1 and MEP2 may result inmeasurement errors in certain instances. (It is noted that intermediatemaintenance points 212-3, 212-4, and 212-5, when configured as MIPs, mayoperate transparently with respect to synthetic loss measurements andmay be configured to pass through synthetic data used during syntheticloss measurements and, accordingly, may not originate and/or evaluatesynthetic data frames.) Specifically, when LAG 220 undergoes an eventthat causes ports 206-1, 206-2 and/or network interfaces 204-1, 204-2 tobe reconfigured with different physical connections and/or hardware, thenewly connected components may not be aware of a previous state of anongoing synthetic loss measurement in which maintenance points 212-1,212-2 serve as MEP1. For example, LAG 220 may change its configurationto use a different one of ports 206-1 and/or ports 206-2. The change inconfiguration may result from a planned operation or as a result of anunpredictable occurrence, for example, an automatic network event, suchas a protection switching event to provide fault tolerance in network100. Because the ports associated with a MEP may locally store framecounts for the synthetic loss measurement, a received and/or transmittedframe count for a conventional synthetic loss measurement may be lost,which may cause measurement values to be lost beyond the individualframes affected. Furthermore, a conventional synthetic loss measurementmay stall or hang when a change in physical and/or logical configurationoccurs at a MEP, which may involve undesirable human intervention toremediate. It is noted that such disruptions to an ongoing conventionalsynthetic loss measurement may occur at any MEP, either local or remote.In various network configurations (not shown), MEPs may be instantiatedat a network interface (i.e., a line card) and/or a network element. Forexample, in an equipment protection configuration, a first line card maybe paired with a second line card at a given local network element,while a local MEP is instantiated on both the first line card and thesecond line card. A remote MEP may be instantiated in this case at aremote line card on a remote network element. The first and second linecards may be coupled to a cross connection, for example, using a switchfabric that enables automatic switchover to the second line card whenthe first line card fails. Similarly, two network elements (e.g., aprimary and a backup) may instantiate a MEP, for example, when the twonetwork elements comprise a portion of a LAG, such that the LAG isprotected from failure of the primary network element by automaticswitchover to the backup network element.

As will be described in further detail, the novel methods and systemsdisclosed herein for performing synthetic loss measurements usingsession numbers have been invented to overcome such disadvantages andenable continuation of synthetic loss measurements with accurate resultswhen either planned or automatic network configuration changes occur innetwork 100.

Referring now to FIG. 3, a transaction diagram of selected elements ofan embodiment of method 300 for dual-ended synthetic loss measurementsis depicted. The transaction diagram in FIG. 3 depicts dual-endedsynthetic loss measurements between local network element 302 (which mayinclude an instantiation of MEP1) and remote network element 304 (whichmay include an instantiation of MEP2), and illustrates actions at eachMEP as well as transactions (i.e., communications) transmitted andreceived between MEP1 and MEP2 where time advances in the downwarddirection. Method 300 may be performed using network segment 200 (seeFIG. 2). It is noted that certain operations described in method 300 maybe optional or may be rearranged in different embodiments. Method 300may depict aspects of dual-ended synthetic loss measurements describedbelow with respect to FIGS. 5A-5C. Symbols that may be used with respectto method 300 are defined in Table 1 below.

TABLE 1 Symbols used in dual-ended synthetic loss measurements (FIG. 3)Symbol (or Variable) Name Definition SN a current and unique sessionnumber specific to an interface at a MEP TxSN1 the transmitting sessionnumber for an interface at a MEP RxSN1 the receiving session number foran interface at a MEP TxFC1 a transmitted frame count for an interfaceat a MEP RxFC1 a received frame count for an interface at a MEP TxFCf atransmitted frame count sent with a 1SL synthetic frame TxSNf atransmitting session number sent with a 1SL synthetic frame

Dual-ended SLM may be performed according to the methods describedherein using an SLM protocol, which may comprise certain rules and/orspecific actions. In dual-ended SLM, MEP1 may send 1SL synthetic framesto MEP2 in one direction, while MEP2 may send 1SL synthetic frames inthe other direction. When a MEP sends a 1SL synthetic frame, the sendingMEP includes the current session number (SN) in an organization specifictype, length, value (TLV) field of the 1SL synthetic frame, TxSNf. Inother words, a MEP may copy SN to TxSNf in the 1SL synthetic frame.(After a new session is initiated, the MEP may copy TxSN1 to TxSNf inthe 1SL synthetic frame.) Both MEP1 and MEP2 maintain two local symbols,TxSN1 and RxSN1 which are initialized to zero. When the MEP receives a1SL synthetic frame, the session conditions for dual-ended SLM, whichmay cause a new session to be initiated, are evaluated. The sessionconditions for dual-ended SLM may include at least one of the followingsession conditions:

Does SN not equal TxSN1? (i.e., local interface change?); and

Does TxSNf from the incoming 1SL synthetic frame not equal RxSN1? (i.e.,remote interface change?).

When at least one of the session conditions is true, a new session isstarted by copying SN to TxSN1 and copying TxSNf from the incoming 1SLsynthetic frame to RxSN1. In this manner, both the transmitting sessionnumber indicative of a local network interface as well as the receivingsession number indicative of the remote network interface are updated.It is noted that values for TxFC1 and/or RxFC1 may or may not be resetwhen a new session is initiated. Computing frame loss at a receiver of a1SL synthetic frame may include calculating a frame loss parameter, suchas a number of lost frames or a percentage of lost frames, for a givensession (i.e., based on identical values for TxSN1, RxSN1), measurementperiod, and/or test identification, for example.

In FIG. 3, method 300 may begin by activating (operation 306-1)interface IF1 at local network element 302 (MEP1) and activating(operation 308-1) interface IF1 at remote network element 304 (MEP2). Inoperation 306-1, interface IF1 at local network element 302 stores thefollowing values: SN=101 and TxSN1=RxSN1=0. In operation 308-1,interface IF1 at local network element 304 stores the following values:SN=201 and TxSN1=RxSN1=0. Then, a 1SL synthetic frame is sent (operation320) from MEP1 to MEP2 with the values: TxFCf=1 and TxSNf=101. Uponreceipt of the 1SL synthetic frame in operation 320, a new session isinitiated (operation 310-1) at MEP2, because both session conditions arefound to be true and MEP2 stores the values: TxSN1=201, RxSN1=101, andRxFC1=1. MEP2 may send (operation 321) a 1SL synthetic frame to MEP1with the values: TxFCf=1 and TxSNf=201. Upon receipt of the 1SLsynthetic frame in operation 321, a new session is initiated (operation310-2) at MEP1, because both session conditions are found to be true andMEP1 stores the values: TxSN1=101, RxSN1=201, and RxFC1=1. Immediatelyafter operation 320, MEP1 may send (operation 322) a 1SL synthetic frameto MEP2 with the values: TxFCf=2 and TxSNf=101. MEP1 may continuesending 1SL synthetic frames to MEP2 while incrementing TxFC1 (notshown) for each 1SL synthetic frame sent and sending this value as TxFCfin each successive 1SL synthetic frame. After sending 98 additional 1SLsynthetic frames (not shown), MEP1 may send (operation 324) a 1SLsynthetic frame to MEP2 with the values: TxFCf=100 and TxSNf=101. MEP2may compute (operation 312-1) frame loss (i.e., calculate a frame lossparameter) for the session given by TxSN1=201 and RxSN1=101 withreceived frame count RxFC1=100. MEP2 may continue computing frame loss(not shown) for this session until a new session is initiated at MEP2(see operation 310-4).

Then in FIG. 3, at some later time, MEP2 may send (operation 323) a 1SLsynthetic frame to MEP1 with the values: TxFCf=94 and TxSNf=201. It isnoted that the frame counts for dual-ended SLM in each direction areindependent of each other. MEP1 may compute (operation 312-2) frame loss(i.e., calculate a frame loss parameter) for the session given byTxSN1=101 and RxSN1=201 with received frame count RxFC1=94. Then, IF2may be activated (operation 306-2) on MEP1, while IF1 is deactivated(operation 306-2) but remains in place and powered on and continues tolocally store TxFC1 and RxFC1. Operation 306-2 may include settingSN=102 for IF2 on MEP1, setting TxSN1=RxSN1=0, and setting SN=109 forIF1 on MEP1. At some later time, MEP2 may send (operation 325) a 1SLsynthetic frame to MEP1 with the values: TxFCf=96 and TxSNf=201.Although from the value of TxFCf it may be inferred that a 1SL syntheticframe from MEP2 to MEP1 corresponding to TxFCf=95 was lost (not shown),the dual-ended SLM may continue irrespectively and may result inaccurate frame loss measurements. Upon receipt of the 1SL syntheticframe in operation 325, a new session is initiated (operation 310-3) atMEP1, because both session conditions are found to be true and MEP1stores the values: TxSN1=102, RxSN1=201, and may also store RxFC1=1 whenthe incoming frame count is reset. In various embodiments, the incomingframe count RxFC1 may not be reset at operation 310-3, because adifference between a final frame count and an initial frame count over ameasurement period may be used for SLM purposes. Then, MEP1 may send(operation 326) a 1SL synthetic frame to MEP2 with the values: TxFCf=1and TxSNf=102. Upon receipt of the 1SL synthetic frame in operation 326,a new session is initiated (operation 310-4) at MEP2, because onesession condition is found to be true and MEP2 stores the values:TxSN1=201, RxSN1=102, and may also store RxFC1=101 when the incomingframe count is not reset. The incoming frame count (RxFC1) may not needto be reset to 1 in operation 310-4 because a difference between a finalframe count and an initial frame count over a measurement period may beused for SLM purposes. In other embodiments (not shown), the incomingframe count RxFC1 may be reset at operation 310-4. At some later time,MEP2 may send (operation 327) a 1SL synthetic frame to MEP1 with thevalues: TxFCf=47 and TxSNf=201. MEP1 may compute (operation 312-3) frameloss (i.e., calculate a frame loss parameter) for the session given byTxSN1=102 and RxSN1=201 with received frame count RxFC1=47. At somelater time, MEP1 may send (operation 328) a 1SL synthetic frame to MEP2with the values: TxFCf=43 and TxSNf=102. MEP2 may compute (operation312-4) frame loss (i.e., calculate a frame loss parameter) for thesession given by TxSN1=201 and RxSN1=102 with received frame countRxFC1=143.

Finally, in FIG. 3, IF1 may be reactivated (operation 306-3) on MEP1,while IF2 is deactivated (operation 306-3). Operation 306-3 may includesetting SN=110 for IF2 on MEP1. It is noted that SN=109, TxSN1=101, andRxSN1=201 may be retained at IF1 upon reactivation in operation 306-3.Then, MEP2 may send (operation 329) a 1SL synthetic frame to MEP1 withthe values: TxFCf=48 and TxSNf=201. Upon receipt of the 1SL syntheticframe in operation 329, a new session is initiated (operation 310-5) atMEP1, because one session condition is found to be true and MEP1 storesthe values: TxSN1=109, RxSN1=201, and RxFC1=95. Note that the value forRxFC1 is retained from a previous session initiated in operation 310-2for IF1 and may not be reset to 1. Because computing frame loss inoperation 312 involves subtracting a final received frame count from aninitial received frame count for a given measurement period for a givensession, the computed difference of frame loss remains correct. Then,MEP1 may send (operation 330) a 1SL synthetic frame to MEP2 with thevalues: TxFCf=44 and TxSNf=109. Upon receipt of the 1SL synthetic framein operation 330, a new session is initiated (operation 310-6) at MEP2,because one session condition is found to be true and MEP2 stores thevalues: TxSN1=201, RxSN1=109, and may also store RxFC1=144 when theincoming frame count is not reset. The incoming frame count (RxFC1) maynot need to be reset to 1 in operation 310-6 because a differencebetween a final frame count and an initial frame count over ameasurement period may be used for SLM purposes. In other embodiments(not shown), the incoming frame count RxFC1 may be reset at operation310-6.

Referring now to FIG. 4, a transaction diagram of selected elements ofan embodiment of method 400 for single-ended synthetic loss measurementsis depicted. The transaction diagram in FIG. 4 depicts single-endedsynthetic loss measurements between local network element 402 (which mayinclude an instantiation of MEP1) and remote network element 404 (whichmay include an instantiation of MEP2), and illustrates actions at eachMEP as well as communications transmitted and received between MEP1 andMEP2 where time advances in the downward direction. Method 400 may beperformed using network segment 200 (see FIG. 2). It is noted thatcertain operations described in method 400 may be optional or may berearranged in different embodiments. Method 400 may depict aspects ofsingle-ended synthetic loss measurements described below with respect toFIGS. 6A-6C. Symbols that may be used with respect to method 400 aredefined in Table 2 below.

TABLE 2 Symbols used in single-ended synthetic loss measurements (FIG.4) Symbol (or Variable) Name Definition SN a current and unique sessionnumber specific to an interface at a MEP TxSN1 the transmitting sessionnumber for an interface at a MEP RxSN1 the receiving session number foran interface at a MEP TxFC1 a transmitted frame count for an interfaceat a MEP RxFC1 a received frame count for an interface at a MEP TxFCf aframe count for a synthetic message sent with the synthetic message andwith a synthetic response TxSNf a transmitting session number for asynthetic message sent with the synthetic message and with a syntheticresponse TxFCb a frame count for a synthetic response send with thesynthetic response TxSNb a transmitting session number for a syntheticresponse sent with the synthetic response

Single-ended SLM may be performed according to the methods describedherein using an SLM protocol, which may comprise certain rules and/orspecific actions. Although single-ended SLM may be performed by any MEP,for descriptive clarity in FIG. 4, MEP1 is the single end that sendssynthetic messages, receives synthetic responses, and computes frameloss. In single-ended SLM, MEP1 may send a synthetic message to MEP2 inone direction, while MEP2 may respond to the synthetic message bysending a synthetic response in the other direction back to MEP1. WhenMEP1 sends a synthetic message, MEP1 includes the current session number(SN) in an organization specific type, length, value (TLV) field of thesynthetic message, TxSNf. In other words, a MEP may copy SN to TxSNf inthe synthetic message. (After a new session is initiated, the MEP maycopy TxSN1 to TxSNf in the synthetic message.) When MEP2 responds to thesynthetic message by sending back a synthetic response, MEP2 copiesTxSNf from the synthetic message to the synthetic response. MEP1maintains two local symbols, TxSN1 and RxSN1 which are initialized tozero. When MEP1 receives a synthetic response, the session conditionsfor single-ended SLM, which may cause a new session to be initiated, areevaluated. The session conditions for single-ended SLM may include atleast one of the following session conditions:

Does TxSNf not equal TxSN1? (i.e., local interface change?); and

Does TxSNb not equal RxSN1? (i.e., remote interface change?).

When at least one of the session conditions is true, a new session isstarted by copying TxSNf to TxSN1 and copying TxSNb to RxSN1. In thismanner, both the transmitting session number indicative of a localnetwork interface (MEP1) as well as the receiving session numberindicative of a remote network interface (MEP2) are updated. It is notedthat values for TxFC1 and/or RxFC1 may or may not be reset when a newsession is initiated. Computing frame loss at MEP1 may includecalculating a frame loss parameter, such as a number of lost frames or apercentage of lost frames for a given session (i.e., based on identicalvalues for TxSN1, RxSN1), measurement period, and/or testidentification, for example.

In FIG. 4, method 400 may begin by activating (operation 406-1)interface IF1 at local network element 402 (MEP1) and activating(operation 408-1) interface IF1 at remote network element 404 (MEP2). Inoperation 406-1, interface IF1 at local network element 402 stores thefollowing values: SN=101 and TxSN1=RxSN1=0. In operation 408-1,interface IF1 at local network element 404 stores the following values:SN=201. Then, a synthetic message is sent (operation 420) from MEP1 toMEP2 with the values: TxFCf=1 and TxSNf=101. MEP1 may send (operation422) a synthetic message to MEP2 with the values: TxFCf=2 and TxSNf=101.Upon receipt of the synthetic message in operation 420, MEP2 generatesand sends (operation 421) a synthetic response with the values: TxFCf=1,TxFCb=1, TxSNf=101, and TxSNb=201. Upon receipt of the syntheticresponse in operation 421, a new session is initiated (operation 410-1)at MEP1, because both session conditions are found to be true and MEP1stores the values: TxSN1=101, RxSN1=201, and RxFC1=1. Upon receipt ofthe synthetic message in operation 422, MEP2 generates and sends(operation 423) a synthetic response with the values: TxFCf=2, TxFCb=2,TxSNf=101, and TxSNb=201. MEP1 may compute (operation 412-1) frame loss(i.e., calculate a frame loss parameter) for the session given byTxSN1=101 and RxSN1=201 with received frame count RxFC1=2. After sometime, MEP1 may send (operation 424) a synthetic message to MEP2 with thevalues: TxFCf=97 and TxSNf=101. Then, before MEP2 may generate asynthetic response to the synthetic message sent in operation 424, IF1may be deactivated (operation 408-2) on MEP2, while IF2 is activated(operation 408-2) on MEP2. Operation 408-2 may include setting SN=202for IF1 on MEP2 and setting SN=209 for IF1 on MEP2. MEP1 may then send(operation 426) a synthetic message to MEP2 with the values: TxFCf=98and TxSNf=101. Upon receipt of the synthetic message in operation 426,MEP2 generates and sends (operation 425) a synthetic response with thevalues: TxFCf=98, TxFCb=1, TxSNf=101, and TxSNb=202. Upon receipt of thesynthetic response in operation 425, a new session is initiated(operation 410-2) at MEP1, because one session condition is found to betrue and MEP1 stores the values: TxSN1=101, RxSN1=202, and RxFC1=97.After some time, MEP1 may send (operation 428) a synthetic message toMEP2 with the values: TxFCf=198 and TxSNf=101. Upon receipt of thesynthetic message in operation 428, MEP2 generates and sends (operation427) a synthetic response with the values: TxFCf=198, TxFCb=100,TxSNf=101, and TxSNb=202. MEP1 may compute (operation 412-2) frame loss(i.e., calculate a frame loss parameter) for the session given byTxSN1=101 and RxSN1=202 with received frame count RxFC1=197. Then, IF1may be deactivated (operation 406-2) on MEP1, while IF2 is activated(operation 406-2) on MEP1. Operation 406-2 may include setting SN=102for IF2 on MEP1, setting TxSN1=RxSn1=0 for IF2 on MEP1, and settingSN=109 for IF1 on MEP1. Then, MEP1 may send (operation 430) a syntheticmessage to MEP2 with the values: TxFCf=645 and TxSNf=102. Upon receiptof the synthetic message in operation 430, MEP2 generates and sends(operation 429) a synthetic response with the values: TxFCf=645,TxFCb=101, TxSNf=102, and TxSNb=202. Upon receipt of the syntheticresponse in operation 429, a new session is initiated (operation 410-3)at MEP1, because both session conditions are found to be true and MEP1stores the values: TxSN1=102, RxSN1=202, and may also store RxFC1=1 whenthe incoming frame count is reset. In various embodiments, the incomingframe count RxFC1 may not be reset at operation 410-3, because adifference between a final frame count and an initial frame count over ameasurement period may be used for SLM purposes. It is noted that TxFCfmay represent a value that IF2 previously retained (not shown) in alocal memory that was not reset in operation 406-2, while TxFCb mayrepresent a received synthetic message count RxFC1 (not shown) at MEP2.After some time, MEP1 may send (operation 432) a synthetic message toMEP2 with the values: TxFCf=945 and TxSNf=102. Upon receipt of thesynthetic message in operation 432, MEP2 generates and sends (operation431) a synthetic response with the values: TxFCf=945, TxFCb=401,TxSNf=102, and TxSNb=202. MEP1 may compute (operation 412-3) frame loss(i.e., calculate a frame loss parameter) for the session given byTxSN1=102 and RxSN1=202 with received frame count RxFC1=300.

Turning now to FIGS. 5A, 5B, and 5C, a block diagram of selectedelements of an embodiment of method 500 for dual-ended synthetic lossmeasurements is depicted in flow-chart form. Method 500 may be performedusing network segment 200 (see FIG. 2). It is noted that certainoperations described in method 500 may be optional or may be rearrangedin different embodiments. Dual-ended synthetic loss measurements(DE-SLM) may involve unidirectional transmission of a one-way syntheticloss message (1SL, also referred to herein as an instance of a“synthetic frame” or simply, a “1SL frame”) between two maintenancepoints (i.e., MEPs). In dual-ended synthetic loss measurements, thereceiver keeps track of the frame count and may calculate a frame lossparameter for characterizing frame loss during a measurement period. Itis noted that dual-ended SLM may be performed in both directionssimultaneously on a given network channel, such that each MEP of thenetwork channel measures frame loss as a receiver in one direction.

In FIG. 5A, method 500-1 may begin by maintaining (operation 502), at alocal maintenance point, a transmitting session number for a firstinterface component included with the local maintenance point and areceiving session number for a second interface component included witha remote maintenance point. The local maintenance point and the remotemaintenance point may be represented by maintenance points 212-1, 212-2(either singly or in combination) and maintenance point 212-6, as shownin FIG. 2. At the first interface component, a first 1SL frame may bereceived (operation 504) from the second interface component, the firstsynthetic frame including a first session number indicative of thesecond interface component. Responsive to receiving the first 1SL framein operation 504, an incoming frame count for the local maintenancepoint may be incremented (operation 505), the incoming frame count beingindicative of a number of 1SL frames received at the local maintenancepoint. Then in method 500-1, a decision may be made whether the firstsession number does not equal (operation 506) the receiving sessionnumber. The evaluation in operation 506 may be indicative of aconfiguration change at the remote maintenance point, such as aprotection switch event. When the result of operation 506 is NO, method500-1 may advance to operation 512 (see FIG. 5B, method 500-2). When theresult of operation 506 is YES, method 500-1 may copy the first sessionnumber to the receiving session number (operation 508). In certainembodiments, an incoming frame count for the local maintenance point maybe reset in conjunction with operation 508 (not shown). After operation508, method 500 may continue with operation 512 in method 500-2 in FIG.5B.

Advancing now to FIG. 5B, method 500-2 may continue method 500 bydetecting (operation 512) deactivation of the first interface componentand activation of a third interface component associated with the localmaintenance point, the third interface component replacing the firstinterface component. It is noted that the deactivation and/or activationin operation 512 may involve a ‘soft’ or logical deactivation, such thatthe first interface component remains installed and powered on and mayretain certain locally stored values, such as a transmitted and/or areceived frame count, and/or other state information with respect to anongoing synthetic loss measurement. The replacement in operation 512 mayalso include a ‘hard’ deactivation and/or activation where the firstinterface component is physically removed and powered down, therebylosing any locally stored values and/or state information with respectto an ongoing synthetic loss measurement. A second session number may beassigned (operation 514) to the third interface component. A thirdsession number different from the second session number may be assigned(operation 516) to the first interface component. The third sessionnumber may be pre-assigned in operation 516 to prevent conflicts withthe second session number and to prepare the first interface componentfor reactivation at a later time, without creating errors in an ongoingSLM. A second 1SL frame may be received (operation 520) from the secondinterface component, the second 1SL frame including the first sessionnumber. Then, a decision may be made (operation 522), whether at leastone session condition is true. The session conditions may be selectedfrom: (a) does the second session number not equal the transmittingsession number?; and (b) does the first session number not equal thereceiving session number? When the result of operation 522 is NO, method500 may continue with operation 530 in method 500-3 (see FIG. 5C). Whenthe result of operation 522 is YES, the second session number may becopied (operation 524) to the transmitting session number and the firstsession number may be copied (operation 526) to the receiving sessionnumber. After operation 526, method 500 may continue with operation 530in method 500-3 in FIG. 5C.

Advancing now to FIG. 5C, method 500-3 may continue method 500 bydetecting reactivation (operation 530) the first interface component anddeactivation of the third interface component. The third session numbermay be copied (operation 531) to the transmitting session number. It isnoted that the first interface component may be reactivated either withor without statefulness with regard to a previously ongoing syntheticloss measurement session that the first interface component wasperforming. A third 1SL frame may be sent (operation 532) from the firstinterface component, the third 1SL frame including the transmittingsession number, the receiving the first 1SL frame and the sending thethird 1SL frame being performed irrespective of changes to thetransmitting session number and the receiving session number. In otherwords, dual-ended synthetic loss measurements may continue withoutsignificant error in method 500 regardless of a configuration change,such as a protection switch event in the network segment between thelocal maintenance point and the remote maintenance point (see also FIG.3). A frame loss parameter may be calculated (operation 534) for ameasurement period based on frame count values, including the incomingframe count, associated with identical values for the transmittingsession number and with identical values for the receiving sessionnumber. The calculation described in operation 534 enables accuratevalues for frame loss irrespective of configuration changes at the localand/or remote maintenance points, and enables synthetic lossmeasurements to continue when configuration changes, such as protectionswitch events, occur. In certain embodiments, a test identificationparameter (e.g., TestID) may additionally be used to specify a pluralityof concurrent SLM sessions, each further correlated using an identicalvalue for the test identification parameter.

Turning now to FIGS. 6A, 6B, and 6C, a block diagram of selectedelements of an embodiment of method 600 for single-ended synthetic lossmeasurements is depicted in flow-chart form. Method 600 may be performedusing network segment 200 (see FIG. 2). It is noted that certainoperations described in method 600 may be optional or may be rearrangedin different embodiments. Single-ended synthetic loss measurements(SE-SLM) may involve transmission of a synthetic loss message (alsoreferred to as SLM) between at least two maintenance points (i.e.,MEPs), and, in response, a return transmission of a synthetic lossresponse (SLR). In single-ended synthetic loss measurements, thereceiver keeps track of the frame counts sent and received and maycalculate a frame loss parameter for characterizing frame loss during ameasurement period. It is noted that single-ended synthetic lossmeasurements may be performed by sending a synthetic loss message to atleast one remote MEP and receiving corresponding responses from theremote MEP(s), such that multiple network channels may be measured forframe loss simultaneously from the local MEP (also referred to asmultipoint service or multicasting).

In FIG. 6A, method 600-1 may begin by maintaining (operation 602), at alocal maintenance point, a transmitting session number for a firstinterface component included with a local maintenance point and areceiving session number for a second interface component included witha remote maintenance point. The local maintenance point and the remotemaintenance point may be represented by maintenance points 212-1, 212-2(either singly or in combination) and maintenance point 212-6, as shownin FIG. 2. At the first interface component, a first synthetic lossmessage may be sent (operation 604) to the second interface component,the first synthetic loss message including a first session numberindicative of the first interface component. At the first interfacecomponent, a first synthetic loss response may be received (operation606) from the second interface component, the first synthetic lossresponse including a second session number and a third session numberindicative of the second interface component. Then, a decision may bemade (operation 608) whether the third session number does not equal thereceiving session number. The decision in operation 608 may correspondto detecting a configuration change, such as a protection switch event,at the second interface component. When the result of operation 608 isNO, method 600 may continue with operation 612 in method 600-2 (see FIG.6B). When the result of operation 608 is YES, the third session numbermay be copied (operation 610) to the receiving session number. Afteroperation 610, method 600 may continue with operation 612 in method600-2 in FIG. 6B.

Advancing now to FIG. 6B, method 600-2 may continue method 600 bydetecting (operation 612) deactivation of the first interface componentand activation of a third interface component associated with the localmaintenance point, the third interface component replacing the firstinterface component. It is noted that the replacement in operation 612may involve a ‘soft’ or logical deactivation, such that the firstinterface component remains installed and powered on and may retaincertain locally stored values, such as a transmitted and/or a receivedframe count, and/or other state information with respect to an ongoingsynthetic loss measurement. The replacement in operation 612 may alsoinclude a ‘hard’ deactivation where the first interface component isphysically removed and powered down, thereby losing any locally storedvalues and/or state information with respect to an ongoing syntheticloss measurement. A fourth session number may be assigned (operation614) to the third interface component. A fifth session number differentfrom the transmitting session number may be assigned (operation 616) tothe first interface component. The fifth session number may bepre-assigned in operation 616 to prevent conflicts with the fourthsession number and to prepare the first interface component forreactivation at a later time, without creating errors in an ongoingsynthetic loss measurement. A second synthetic loss message may be sent(operation 620) from the third interface component to the secondinterface component, the second synthetic message including the fourthsession number indicative of the third interface component. A secondsynthetic loss message may be received (operation 622) from the secondinterface component, the second synthetic loss response including asixth session number and a seventh session number indicative of thesecond interface component. Then, a decision may be made (operation 624)whether the sixth session number does not equal the transmitting sessionnumber. When the result of operation 624 is NO, method 600 may continuewith operation 630 in method 600-3 (see FIG. 6C). When the result ofoperation 624 is YES, the sixth session number may be copied (operation626) to the transmitting session number. After operation 626, method 600may continue with operation 630 in method 600-3 in FIG. 6C.

Advancing now to FIG. 6C, method 600-3 may continue method 600 bycalculating (operation 630) a frame loss parameter based on frame countvalues for a measurement period, the frame count values being associatedwith identical values for the transmitting session number and withidentical values for the receiving session number. Irrespective ofchanges to the transmitting session number and the receiving sessionnumber, method 600 may continue (operation 632) sending syntheticmessages and receiving synthetic responses.

The above disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments which fall within thetrue spirit and scope of the present disclosure. Thus, to the maximumextent allowed by law, the scope of the present disclosure is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

What is claimed is:
 1. A method for performing single-ended syntheticloss measurements, comprising: maintaining, at a local maintenancepoint, a transmitting session number for a first interface componentassociated with the local maintenance point and a receiving sessionnumber for a second interface component associated with a remotemaintenance point; sending, from the first interface component, a firstsynthetic loss message to the second interface component, wherein thefirst synthetic loss message includes a first session number indicativeof the first interface component; receiving, at the first interfacecomponent, a first synthetic loss response from the second interfacecomponent, wherein the first synthetic loss response includes a secondsession number and a third session number indicative of the secondinterface component; and when the third session number does not equalthe receiving session number, copying the third session number to thereceiving session number.
 2. The method of claim 1, further comprising:responsive to detecting deactivation of the first interface componentand activation of a third interface component associated with the localmaintenance point, wherein the third interface component replaces thefirst interface component: assigning a fourth session number to thethird interface component; and assigning a fifth session number to thefirst interface component, wherein the fourth session number and thefifth session number are different from the transmitting session number.3. The method of claim 2, further comprising: sending, from the thirdinterface component, a second synthetic loss message to the secondinterface component, wherein the second synthetic loss message includesthe fourth session number indicative of the third interface component;and responsive to receiving, from the second interface component, asecond synthetic loss response at the third interface component, whereinthe second synthetic loss response includes a sixth session number and aseventh session number indicative of the second interface component, andwhen the sixth session number does not equal the transmitting sessionnumber, copying the sixth session number to the transmitting sessionnumber.
 4. The method of claim 1, further comprising: calculating aframe loss parameter based on frame count values for a measurementperiod, wherein the frame count values used to calculate the frame lossparameter are associated with identical values for the transmittingsession number and with identical values for the receiving sessionnumber.
 5. The method of claim 4, wherein the frame count values used tocalculate the frame loss parameter are associated with identical valuesfor a test identification parameter.
 6. The method of claim 1, whereinthe sending the first synthetic loss message and the receiving the firstsynthetic loss response are performed irrespective of changes to thetransmitting session number and the receiving session number.
 7. Themethod of claim 1, wherein the first synthetic loss message includes thefirst session number in an organization-specific type, length, and value(TLV) field in accordance with the International Telecommunication Union(ITU) Y.1731 standard, and wherein the first synthetic loss responserespectively includes each of the second session number and the thirdsession number in an organization-specific type, length, and value (TLV)field in accordance with the International Telecommunication Union (ITU)Y.1731 standard.
 8. The method of claim 1, wherein the sending, from thefirst interface component, the first synthetic loss message includessending the first synthetic loss message to a plurality of interfacecomponents associated with a respective plurality of remote maintenancepoints, the plurality of interface components including the secondinterface component.
 9. The method of claim 1, wherein a network segmenttransmitting the first synthetic loss message between the firstinterface component and the second interface component includes at leastone link aggregation group (LAG).
 10. A system for performingsingle-ended synthetic loss measurements, comprising: a processorconfigured to access non-transitory computer readable memory media,wherein the memory media store processor-executable instructions, theinstructions, when executed by a processor, cause the processor to:maintain, at a local maintenance point, a transmitting session numberfor a first interface component associated with the local maintenancepoint and a receiving session number for a second interface componentassociated with a remote maintenance point; send, from the firstinterface component, a first synthetic loss message to the secondinterface component, wherein the first synthetic loss message includes afirst session number indicative of the first interface component;receive, at the first interface component, a first synthetic lossresponse from the second interface component, wherein the firstsynthetic loss response includes a second session number and a thirdsession number indicative of the second interface component; and whenthe third session number does not equal the receiving session number,copy the third session number to the receiving session number.
 11. Thesystem of claim 10, wherein the memory media store instructions to:responsive to detecting deactivation of the first interface componentand activation of a third interface component associated with the localmaintenance point, wherein the third interface component replaces thefirst interface component: assign a fourth session number to the thirdinterface component; and assign a fifth session number to the firstinterface component, wherein the fourth session number and the fifthsession number are different from the transmitting session number. 12.The system of claim 11, wherein the memory media store instructions to:send, from the third interface component, a second synthetic lossmessage to the second interface component, wherein the second syntheticloss message includes the fourth session number indicative of the thirdinterface component; and responsive to receiving, from the secondinterface component, a second synthetic loss response at the thirdinterface component, wherein the second synthetic loss response includesa sixth session number and a seventh session number indicative of thesecond interface component, and when the sixth session number does notequal the transmitting session number, copy the sixth session number tothe transmitting session number.
 13. The system of claim 10, wherein thememory media store instructions to: calculate a frame loss parameterbased on frame count values for a measurement period, wherein the framecount values used to calculate the frame loss parameter are associatedwith identical values for the transmitting session number and withidentical values for the receiving session number.
 14. The system ofclaim 13, wherein the frame count values used to calculate the frameloss parameter are associated with identical values for a testidentification parameter.
 15. The system of claim 10, wherein theinstructions to send the first synthetic loss message and theinstructions to receive the first synthetic loss response are performedirrespective of changes to the transmitting session number and thereceiving session number.
 16. The system of claim 10, wherein the firstsynthetic loss message includes the first session number in anorganization-specific type, length, and value (TLV) field in accordancewith the International Telecommunication Union (ITU) Y.1731 standard,and wherein the first synthetic loss response respectively includes eachof the second session number and the third session number in anorganization-specific type, length, and value (TLV) field in accordancewith the International Telecommunication Union (ITU) Y.1731 standard.17. The system of claim 10, wherein the instructions to send, from thefirst interface component, the first synthetic loss message includeinstructions to send the first synthetic loss message to a plurality ofinterface components associated with a respective plurality of remotemaintenance points, the plurality of interface components including thesecond interface component.
 18. The system of claim 10, wherein anetwork segment transmitting the first synthetic loss message betweenthe first interface component and the second interface componentincludes at least one link aggregation group (LAG).